1. Field of the Invention
This application relates to methods and systems for treating fluids recovered from a subsurface oil or gas production process. More specifically, this application relates to methods and systems of treating flow back and/or production brine and preparing hydraulic fracturing fluids comprising the treated flow back and/or production brine.
2. Description of Related Art
Hydraulic fracturing, also referred to as “hydrofracking,” is a technique commonly used in the removal of oil and gas from subsurface rock formation reservoirs, and especially shale reservoirs. Hydraulic fracturing works by increasing the pressure in the formation rock so that fractures form. The fractures in the formation rock provide a pathway through which gas or oil can travel to the well bore. Fracture formation across a wide underground area also increases the area of the reservoir which can be accessed by a single well bore. Absent the formation of fractures in the rock formation, the porosity and permeability of the rock may be too low to allow for oil and gas to be recovered therefrom at an economic rate. This is especially true of shale reservoirs, which typically have an extremely low natural permeability.
Hydraulic fractures are traditionally created by pumping a fracturing fluid into a wellbore at a rate sufficient to increase the pressure downhole to a value in excess of the fracture strength of the formation rock. The increased pressure due to the high-pressure pumping of the fracturing fluid causes cracks to form in the formation. The fracturing fluid then can enter these cracks and extend the crack further into the formation. Often times, a solid proppant is added to the fracture fluid to keep the cracks open after injection ceases.
Significant amounts of fracturing fluid, e.g., 1,000,000 gallons or more per well, may be needed to create the pressure necessary to cause fractures to occur. The fracturing fluid is typically primarily composed of water, which may be unavailable locally. The costs associated with transporting and storing water from other sources can greatly impact the economic viability of hydrofracturing-based oil and gas recovery.
In a typical operation of a gas well that undergoes hydraulic fracturing, water is expelled from the rock formation after injection of the fracturing fluid and subsequent thereto during the production of gas as part of the produced fluid from the well. This water may initially be a return of the fracturing fluid, often referred to as flow back water. Then, the produced fluid may transition to a content that is primarily natural formation water, or connate water, present in the formation that is forced to the surface as a result of the hydrofracturing operation, also referred to as production brine. The produced fluid recovered at the surface may contain contaminants, such as minerals that were part of the subsurface formation as well as chemicals that were injected as part of the fracturing fluid. Treatment and disposal of this produced fluid can add to the complexity and cost of the well's operation, typically requiring capturing and shipping the fluid to treatment facilities. While methods of reusing the produced fluid in a productive way have been explored in the past, the industry is constantly searching for improved uses of the produced water.